It is customary to produce flat glass products in large sheets, or as a continuous sheet. Such large glass sheets are then trimmed and separated into smaller units of desired size for use.
In general, the separation procedure, while subject to many variations in detail, may be stated as (1) creating a controlled defect in a glass sheet (scoring) and (2) extending that defect to separate the glass (breaking). Scoring may be by any means that induces or creates a crack, or other controlled defect. The crack or defect may be extended to separate the glass by bending to stress the glass, by tapping on the surface opposite a score line, or by thermal separation.
Most applications, where large quantities of sheet glass are scored and broken, require only moderate dimensional and surface quality. Therefore, currently available separation processes usually result in small scratches in the sheet surface, form non-square edges and produce many small chips.
Recently, a strong need has developed for relatively large quantities of precision glass panels. Such glass panels are required to have square edges and to be relatively chip free. More particularly, precision panels are required for fabricating active matrix liquid crystal displays. For this product, any chip larger than five microns in height and 25 microns in length is currently unacceptable. These stringent requirements are expected to become even more stringent as the technology progresses.
None of the high speed processes for breaking scored sheet glass, now in commercial use, satisfy the criteria for high quality panels, that is, chip free and square edges. Hand breaking may be used, but is obviously time-consuming and expensive. Therefore, a high speed process, capable of separating sheet glass into precision panels meeting the indicated requirements, is desperately needed.
It is then a basic purpose of this invention to meet that need. More particularly, it is a purpose of the invention to provide a process for producing precision glass panels in a high speed automatic operation. A further purpose is to supply precision glass panels for fabricating flat glass display products.